Refining kerosenes and gas oil by ternary azeotropic distillation with furfural and water



June 10, 1952 G. B. ARNOLD ETAL 2,600,182

REFINING KEROSENES AND GAS OIL BY TERNARY AZEOTROPIC DISTILLATION WITH FURFURAL AND WATER Filed May l2, 1948 ATTORNEYS' Patented June 10, 1952 UNITED STATES PATENT OFFICE REFINING KEROSENES AND GAS OIL BY TERNARY AZEOTROPIC DISTILLATION WITH FURFURAL AND WATER Application May 12, 1948, Serial No. 26,688

4 Claims.

This invention relates to refining or oil involving azeotropic distillation with a solvent liquid Which is at least partially miscible with water at ordinary temperatures and particularly relates to the treatment of oil containing at least a small proportion of constituents having true boiling points in the range of the solvent boiling temperature and below.

In accordance with the invention, low boiling oil, such as kerosene and gas cils, is extracted with a selective solvent such as furfural in the presence of water or another suitable azeotroping agent in a distilling zone under conditions effective to form a ternary azeotrope withv the desired oil constituents of the feed oil. The distillate containing the azeotrope and a residual liquid containing residue oil are separately withdrawn from the distillation zone.

The invention has application to the reiining of kerosenes and gas oils to remove aromatic constituents, unsaturated hydrocarbons, including naphthenes as well as olens, and sulfur compounds. The resulting refined oils are thus more parafiinic in character and therefore more suitable as burning oils and diesel oils, as the case may be.

According to one mode of operation, the azeotropic distillate is condensed and cooled to approximately atmospheric temperature or to a temperature of about 100 F. and subjected to settling, so that separation into three liquid layers occurs. Thus when water is used as the azeotroping agent, the three layers so formed,I upon settling, comprise an oil-rich liquid layer, a Water-rich liquid layer, and 'a solvent-rich liquid layer. The solvent-rich liquid is recycled to the distillation zone, and residual solvent is recovered from the oil-rich and water-rich liquids leaving a solvent-free rened oil as Will be described later in more detail.

According to another modication of the process of the invention, the -azeotropic distillate is condensed, either Without substantial reduction in temperature or without cooling, to a temperature at which two phase separation occurs. The hot condensate so obtained is subjected to settling in a primary settling zone wherein displacement of oil from water occurs. The displaced oil, retaining a large amount of solvent, is separately subjected to settling in a secondary settling zone at a temperature substantially below the temperature of mis-cibility of its constituentsI so as to eiect recovery of the solvent in concentrated form suitable for recycling'to the distillation zone. Residual solvent is recoveredy from this 2 secondary oil layer and yalso from the primary Water-rich liquid by distillation as will be discussed later.

A further modiiication of the process of the invention involves -carrying out the primary azeotropic distillation so as to form a residual liquid which comprises a solution of residue oil in solvent. This residual liquid solution is subjected to -azeotropic distillation to effect recovery of solvent and produce substantially solventfree residue oil in a manner which will be described in more detail.

In Patent No. 2,534,382, dated Dee. 19, 1950, to William E. Skelton and George B. Arnold, one of the present joint applicants, there is disclosed a process for rening light oils which involves conventional liquid-liquid solvent extraction of the oil coupled with azeotropic distillation of the resulting raffinate and extract phase mixtures for recovery of the solvent. In these operations, however, azeotropic distillation is utilized only to eiect recovery of the solvent from either the raffinate or extract oil or both. The present invention distinguishes therefrom by employing azeotropi-c distillation in eiiecting the initial separation of the feed oil into refined oil and residue analogous to rafnate and extract phases of solvent refining. The present invention also distinguishes from aZeotropic-extracti've/ distillations as heretofore practiced by conducting the operation in the presence of a sufcient amount of water or other Iagent so as to. form a ternary azeotrope rather than a binary azeotrope with all of the raffinate phase discharged from the primary extraction zone.

Ternary azeotropic distillation involves considerably more than merely adding Water to a binary distillation. Binary azeotropes and ternary azeotropes have 'different properties and different limitations.

Binary azeotropes of a solvent and. hydrocarbons boiling above the boiling point ofthe solvent all boil a few degrees lower than they true boiling point of the solvent. Ternary azeotropes. on the other hand, consisting of Water, furfural and hydrocarbon, all boil in the range about 208 to 210 F. under standard conditions of pressure.

Binary azeotropes ofr a solvent and hydrocarbons boiling below or in a range including. the boiling point of the solvent boil over a range a few degrees below the true boiling range of the hydrocarbons. Ternary azeotropes of these hydrocarbons with water and iurfural, on. the other hand, boil. below the boiling point of water, re-

gardless of the boiling point of the hydrocarbons boiling above 212 F.

Separation of hydrocarbon mixtures by binary azeotropic distillation is in general limited to fractions of relatively narrow boiling range. Ternary azeotropic distillation may be applied t hydrocarbon fractions of relatively wide boiling range. Ternary azeotropic distillation using water permits the separation of hydrocarbon mixtures whose boiling range is above the boiling point of water. and which may include the boiling point of the solvent.

In order to describe the invention, reference will now be made to Figures 1 and 2 of the accompanying drawing. The drawing sets forth a method of flow which is particularly suitable for the refining of kerosene using furfural as a selective solvent and water to form the ternary azeotropes.

As indicated in the drawing, kerosene is conducted from a source not shown through a pipe I and introduced to about the mid-point of a distillation column. The furfural is supplied either through pipe 3 leading to the upper portion of the column or through pipes 4 and 5 into the intermediate portion of the tower along with the feed oil. The solvent is introduced to the column in the proportion of about one-half to one volume per Volume of kerosene, and, preferably, in the proportion of about one volume per volume of kerosene.

The column is provided with a reboler 6 to provide heat for distillation. It will be understood that provision can be made for preheating the entering solvent and oil by suitable heat exchange or direct heating, such provision not being indicated in the drawing.

Columnl can be operated under atmospheric or elevated pressures and can also be operated so that the residual liquid drawn olf from the bottom of the tower consists of solvent-free or substantially solvent-free residue oil which can be discharged through pipe 1.

When so operated as to produce solvent-free residue oil, the temperature at the top of the column 2 is maintained at about 275 F., while solvent and kerosene are introduced in the approximate relative proportions of one to one. Water is supplied in the proportion of about oneeighth to one of solvent plus kerosene. Under such conditions, the distillate produced from the column will consist of ternary azeotropes or refined oil hydrocarbons, furfural and water, the refined oil amounting to approximately 5080% by volume of the feed oil. This distillate is discharged through pipe II'I and a condenser cooler II. The resulting cooled condensate at a temperature of about 100 to 150 F. is conducted through pipe I2 to a settling vessel I3.

In the vessel I3, separation into an oil-rich liquid layer, water-rich liquid layer, and a solvent-rich liquid layer occurs. The solvent-rich liquid is continuously drawn off through pipe I5 for return to the column 2. This recycled solvent is saturated with water, and will thus contain about 4-7% water by volume. It may also retain a small amount of residual oilapproximately 5 to 15% by volume.

The refined oil layer containing about 4 to 10% furfural is continuously drawn off through pipe I6 to a secondary column Il wherein it is subjected to azeotropic distillation in the presence of water. This column is also provided with a reboiler I8, and provision is made for supplying water reflux to the top of the column. Thus a portion of the previously mentioned water-rich liquid drawn off through pipe I4 from the settler I3 is conducted through branch pipe I9 to supply this relux liquid. If desired, a further portion of this water may be injected from branch pipe 20 into the lower portion of the column I'I to provide a stripping action to aid in distilling residual solvent from the raffinate oil. Solventfree refined oil is discharged through pipe 2I.

The resulting distillate comprising water, oil and residual solvent is removed through pipe 22, condenser 23 and pipe 24 to the previously mentioned settler I3.

As indicated, a portion of the water-rich liquid from pipe I4 is diverted through pipe 30 and branch pipe 3I communicating with pipes 32 and 33. Pipe 32 thus permits supplying some of this water as reflux to the primary column 2, while pipe 33 permits supplying some of it to the lower portion thereof for stripping purposes. If desired, provision may be made for introducing open steam from a source not shown through pipe 34.

The surplus water not recycled to columns 2 and I1 is discharged through pipe 35. Since it still retains a small amount of residual solvent, it can be passed to a suitable fractionator for the recovery of this residual solvent.

By way of example, when operating in the manner just described, a kerosene feed oil having the following physical characteristics was charged to the middle of the column 2:

Gravity-A. P. I. 40.4 Aniline point 130.5 Sulphur weight, per cent 0.19

Refractive index 1.4551

Color, A. S. T. M 2%;

Distillation-A. S. T. M.:

I. B. P. 360 10% 384 50% 401 440 End point 494 Furfural was charged to the column at the rate of 423 volumes per hour, while the kerosene was charged at the rate of 397. Water was injected at the top of the column at the rate of 10 Volumes per hour, and at the bottom of the column at the rate of 104 volumes per hour.

The temperature at the top of the tower was maintained at about 266 F., the pressure being approximately atmospheric. The resulting distillate was condensed, cooled, and subjected to separation of F. The resulting oil-rich phase amounted to 225 volumes, the water-rich phase, 95, and the furfural-rich phase, 475 volumes per hour. 'Ihe residue oil drawn off from the bottom of the column amounted to 361 volumes per hour.

The oil recovered from the distillate oil-rich phase possessed the following characteristics:

Gravity-API. 44.0 Aniline point 143.6 Sulphur weight, per cent 0.077 Refractive index 1.4445 Color, Saybolt +30 In the event that the primary column 2 is operated so that the residual liquid removed from the bottom thereof comprises a solution of residue oil in solvent, this residual liquid stream is conducted through pipe 40 to a distilling column 4I substantially similar to those previously described, and wherein the residual liquid is subjected to ternary azeotropic distillation in a substantially similar manner to that conducted in column l1, and so as to produce solvent-free residue oil. The latter is discharged through pipe 42.

The resulting distillate is removed through pipe l43, condenser cooler 44 and pipe 45 to a settler 46. In this settler, separation into three liquid layers occurs. The solvent-rich liquid is withdrawn from the bottom of settler 46 through pipe 41 and recycled to the primary column 2.

The water-rich liquid is drawn off through pipe 48, part being diverted through pipe 49 for recycling to column 4| by means of branch pipes 50 and 5l. The non-recycled portion is discharged through pipe 52. It can be treated along with that discharged through pipe 35 in a nal fractionator to recover residual solvent. The oil-rich layer collecting in settler 45 may be discharged as such through pipe 53 in which case it can be conducted through pipe 54 to the residue oil stream discharged through pipe 42. It can also be recycled to the system, for example, by passage through pipe 55 communicating with pipe l or by passage through pipe 55 to be combined with refined oil in pipe l2.

Figure 2 refers to the modification wherein the distillate from the primary column is subjected to staged settling at different temperatures. In this operation, the distillate drawn oir through pipe I 0 is subjected to condensing in condenser II to form a hot condensate at a temperature of about 250 F., and such that water separates from. the oil-furfural mixture.

The hot condensate is passed to a primary settler 60 maintained at about 250 F. and under sufficient pressure to maintain liquid phase conditions therein. In this settler, the mixture separates into a primary oil layer comprising about equal parts by volume of oil and furfural plus a fraction of a per cent of water and a lower layer or aqueous layer comprising about 85% water, 14% furfural and 1% oil. The temperature in the primary settler is chosen so as to effect binary phase separation, the oil-solvent phase being substantially free from Water or containing not more than about 1% by volume.

The aqueous layer is drawn oi through a pipe 6l, and a substantial portion thereof is diverted through pipe 3| for return to the refining tower 2 as has been described in connection with Figure 1.

The primary oil layer is drawn ofi' from the upper portion of the settler 60 through a pipe 62 and passed through a cooler 63 wherein it is cooled to about 100 to 125 F. such that separation into two layers occurs in a settler i64. The upper or secondary oil layer comprises about 94% oil and 6% furfural. The bottom or solvent layer comprises about 85% furfural and 15% oil. This furfural layer is drawn off through pipe 65 and returned to the rening tower 2 as recycled solvent.

The secondary oil layer is drawn orf from the settler 64 through a pipe 66 to the distilling column l1 which has been described in connection with Figure 1. As in the case of Figure 1, the refined oil is drawn off from the bottom of the column I1 while the small amount of residual solvent recovered as distillate therefrom is conducted through pipe 22, cooler 23 and pipe 24 for return to the primary settler 6D.

A portion of the aqueous layer from the bottom of the primary settler 60 is conducted through pipe 66 for introduction to the tower l1 in a manner similar to that already described in connection with Figure 1. Likewise, the nonrecycled or surplus portion of the aqueous layer from the primary settler 60 is drawn off through pipe 35 to a fractionator for recovery of the small amount of residual solvent contained therein.

The extractive-azeotropic distillation operation in the rening tower 2 may be carried out under super-atmospheric pressure; for example, it may be carried out under pressures of ten to twenty-five pounds per square inch gage or sufficient to provide the pressure necessary to maintain liquid phase conditions in the staged settling zones described in Figure 2.

While mention has been made of subjecting the oil-rich liquid streams from the settling vessel I3 to azeotropic distillation, nevertheless, it is contemplated that other procedures may be employed for recovering the residual solvent from the refined oil, such as water washing. The resulting washed water containing extracted solvent should then be treated in a separate fractionator for concentration of the solvent, or contacted with a stream of feed oil under conditions such that the feed oil would extract the furfural from the water.

In operation the primary azeotropicreiining column 2 is operated under conditions to permit maintaining the highest top tower temperature compatible with good rening action. The solvent recovery columns l1 to 4I are operated at the highest temperature compatible with a reasonable amount of oil in the distillate not in excess of about 30%.

Although -treatment of kerosene has been specifically referred to in connection with the drawing, it should be understood that the process is applicable to the treatment of other low boiling oils, including gas oils and oils of either virgin or cracked type. In general, the invention has application to the treatment of hydrocarbon mixtures having an A. S. T. M.boiling range of about 275 to 600. It is also contemplated that it has application to the treatment of oils derived from animal and vegetable sources. Specific conditions of temperature and solvent dosage may vary from those specifically mentioned, depending upon the character of the feed oil undergoing treatment and the degree of fractional separation desired.

Other solvents besides furfural may be used. It is contemplated using relatively high boiling organic solvent liquids which are miscible, at least to some extent, with water at a temperature of about F., and with which the refined oil constituents of the oil feed in the presence of Water form azeotropes. In place of furfural, other members of the furan group may be used as well as other aldehydes such as benzaldehyde. Other solvent compounds are nitrobenzene, ketones, phenols and amines.

Obviously many modifications and variations of the invention as above set forth may be made Without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. In the rening of a mineral feed oil boiling within the range about 275 to 600 F. containing both saturated and unsaturated constituents, said saturated constituents being capable of entering into ternary azeotrope' formation with furfural in the presence of water, to separate therefrom a fraction enriched in said saturated constituents by azeotropic distillation with a polar solvent liquid comprising furfural, the method comprising continuously passing fresh feed oil and said polar solvent to a primary distillation zone, subjecting said oil to azeotropic distillation therein in the presence of water and said solvent, supplying water and said solvent to said primary distillation zone in amounts sufcient to form a distillate consisting essentially of a ternary azeotropic mixture of water, solvent and saturated constituents of oil, and containing at least about 50% of the feed oil entering the extraction zone, and said azeotropic mixture boiling below the boiling temperature of water under the pressure prevailing in said zone, continuously and separately withdrawing from said zone said distillate and a residual liquid containing unsaturated constituents of the feed oil, condensing said distillate, subjecting resulting condensate to stratication in a settling zone at a temperature in the range about 100 to 150 F., forming in said settling zone a water-rich liquid layer, an oil-rich liquid layer and a solvent-rich liquid layer, recycling at least a portion of said solvent-rich liquid to said primary distillation zone, passing said oil-rich liquid to a secondary distillation zone, injecting a portion of said water-rich liquid as reilux to said secondary distillation zone, subjecting the oil-rich liquid to azeotropic distillation therein to remove aqueous solvent as a distillate therefrom, recycling said last mentioned distillate to the aforesaid settling zone and withdrawing substantially solvent-free oil as residual liquid from said secondary distillation zone.

2. The method according to claim 1 in which another portion of said water-rich liquid is passed to the lower section of said secondary distillation zone.

3. In the reiining of a feed oil of the class of kerosene and gas oil containing parainic and relatively non-parafnnic constituents to separate therefrom a fraction enriched in parainic constituents by azeotropic distillation in the presence of water and a polar solvent liquid comprising furfural, the method comprising continuously passing fresh feed oil to a primary distillation zone, subjecting said oil to azeotropic distillation therein in the presence of water and said solvent, supplying said water and solvent to said zone in amounts suflicient to form a distillate consisting Vessentially of a ternary azeotropic mixture of water, solvent and paraflinic constituents of the oil and containing at least the major portion of the parafilnic constituents of the feed oil, continuously and separately withdrawing from said zone said distillate and a residual liquid containing non-parainic constituents of the feed oil, condensing said distillate, subjecting the condensate to stratification in a settling zone at a temperature in the range about 100 to 150 F., forming in said settling zone water-rich, oil-rich and solvent-rich liquid layers, respectively, recycling at least a, portion of said solvent-rich liquid to the extraction zone, passing said oil-rich liquid to a secondary distillation zone, injecting a portion of said water-rich liquid as reflux to said secondary distillation zone, subjecting the oil-rich liquid to azeotropic distillation therein to remove aqueous solvent as a distillate therefrom, recycling said last mentioned distillate to the aforesaid settling zone and withdrawing substantially solvent free oil as residual liquid from said secondary distillation zone.

4. The method according to claim 3 in which another portion of said water-rich liquid is passed to the lower portion of said secondary distillation zone.

GEORGE B. ARNOLD. LOUIS KOVACH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,892,771 Jaeger et al. Jan. 3, 1933 2,162,963 McKittrick June 20, 1939 2,177,183 Kraft et a1. Oct. 24, 1939 2,265,220 Sullivan Dec. 9, 1941 2,290,636 Deanesly July 21, 1942 2,358,128 Lake Sept. 12, 1944 2,361,493 Patterson Oct. 31, 1944 2,368,597 Morris et al.A Jan. 30, 1945 2,376,870 Engel May 29, 1945 2,380,019 Bloomer July 10, 1945 2,388,040 Clark Oct. 30, 1945 2,397,839 Clark Apr. 2, 1946 2,416,377 Chadder Feb. 25, 1947 2,437,649 Milner Mar. 9, 1947 2,445,944 Engel July 27, 1948 2,475,147 Manleyr July 5, 1949 2,497,588 Davies Feb. 14, 1950 

1. IN THE REFINING OF A MINERAL FEED OIL BOILING WITHIN THE RANGE ABOUT 275 TO 600* F. CONTAINING BOTH SATURATED AND UNSATURATED CONSTITUENTS SAID SATURATED CONSTITUENTS BEING CAPABLE OF ENTERING INTO TERNARY AZEOTROPE FORMATION WITH FURFURAL IN THE PRESENCE OF WATER, TO SEPARATE THEREFROM A FRACTION ENRICHED IN SAID SATURATED CONSTITUENTS BY AZEOTROPIC DISTILLATION WITH A POLAR SOLVENT LIQUID COMPRISING FURFURAL, THE METHOD COMPRISING CONTINUOSLY PASSING FRESH FEED OIL AND SAID POLAR SOLVENT TO A PRIMARY DISTILLATION ZONE, SUBJECTING SAID OIL TO AZEOTROPIC DISTILLATION THEREIN IN THE PRESENCE OF WATER AND SAID SOLVENT, SUPPLYING WATER AND SAID SOLVENT TO SAID PRIMARY DISTILLATION ZONE IN AMOUNTS SUFFICIENT TO FORM A DISTILLATE CONSISTING ESSENTIALLY OF A TERNARY AZEOTROPIC MIXTURE OF WATER, SOLVENT AND SATURATED CONSTITUENTS OF OIL, AND CONTAINING AT LEAST ABOUT 50% OF THE FEED OIL ENTERING THE EXTRACTION ZONE, AND SAID AZEOTROPIC MIXTURE BOILING BELOW THE BOILING TEMPERATURE OF WATER UNDER THE PRESSURE PREVAILING IN SAID ZONE, CONTINUOUSLY AND SEPARATELY WITHDRAWING FROM SAID ZONE SAID DISTILLATE AND A RESIDUAL LIQUID CONTAINING UNSATURATED CONSTITUENTS OF THE FEED OIL, CONDENSING SAID DISTILLATE, SUBJECTING RESULTING CONDENSATE TO STRATIFICATION IN A SETTLING ZONE AT A TEMPERATURE IN THE RANGE ABOUT 100 TO 150* F., FORMING IN SAID SETTING ZONE A WATER-RICH LIQUID LAYER, AN OIL-RICH LIQUID LAYER AND A SOLVENT-RICH LIQUID LAYER, RECYCLING AT LEAST A PORTION OF SAID SOLVENT-RICH LIQUID TO SAID PRIMARY DISTILLATION ZONE, PASSING SAID OIL-RICH LIQUID TO A SECONDARY DISTILLATION ZONE, INJECTING A PORTION OF SAID WATER-RICH LIQUID AS REFLUX TO SAID SECONDARY DISTILLATION ZONE, SUBJECTING THE OIL-RICH LIQUID TO AZEOTROPIC DISTILLATION THEREIN TO REMOVE AQUEOUS SOLVENT AS A DISTILLATE THEREFROM, RECYCLING SAID LAST MENTIONED DISTILLATE TO THE AFORESAID SETTLING ZONE AND WITHDRAWING SUBSTANTIALLY SOLVENT-FREE OIL AS RESIDUAL LIQUID FROM SAID SECONDARY DISTILLATION ZONE. 